The present invention relates to the field of electronic article surveillance (EAS) systems, and in particular, to reducing noise interference and probability of false alarm in constant noise environments.
EAS systems are often referred to as anti-theft systems and function in essentially the following manner. An electronic marker or tag is attached to individual items of retail merchandise either in-store or during the manufacturing or packaging process. When a product is legitimately sold, the tags are removed or deactivated at the point of sale and the merchandise can leave the store without triggering an alarm. If, however, a thief attempts to exit the store with an item bearing the xe2x80x9clivexe2x80x9d electronic marker, an alarm is triggered.
A transmitter at a store exit sends out electromagnetic wave pulses. The transmitter""s electromagnetic wave pulses trigger a resonator within any tag located in the transmitter""s detection field. The tag that enters this detection field responds to this pulse by emitting a single frequency signal, much like a tuning fork. When a receiver, also located at the store exit, picks up this return frequency after a predetermined anticipated delay, an alarm is triggered.
All retail stores, however, are filled with electromagnetic noise that can negatively affect a system""s performance and even produce a false alarm. The difference sources of noise include fluorescent lights, computers, neon signs, and vertical main lines among others. These noise sources actually emit noise themselves and can cause poor detection and false alarms. Some sources of noise are referred to as xe2x80x9cperiodicxe2x80x9d interferences, since they occur at regular or constant intervals. When an EAS system is transmitting signals at regular or periodic intervals, there is a possibility that one or more of these periodic interferences will cause a false alarm. The EAS system failed to distinguish if the detected signal is that of an EAS tag or a noise source. In addition to periodic interferences, there are random sources of interference that do not occur at normal or regular intervals.
The prior art of the Ultra-Max(copyright) system of Sensormatic, Inc., is a well-known system recognized by the retail community and a trademark of Sensormatic. Although the Ultra-Max operates at a narrow frequency pulse at 58 kHz, the Ultra-Max transmitter transmits signals periodically into a surveillance area, where electronic tags could be located. Because the signals are transmitted periodically, versions of the Ultra-Max system are more vulnerable to periodic noise sources.
An improved EAS system is the Ultra-Post system of Sensormatic, Inc. This system, unlike the Ultra-Max system, employs a plurality of transmitting modes. Like the Ultra-Max system, this system initially transmits signals at regular or periodic intervals. But once the system detects the presence of a tag at a particular location in the area, the system switches into a second mode of operation, the verification transmitting mode. The system verifies whether what it is detecting is really a tag, and not noise. Even though it performs well in certain environments, the Ultra-Post system requires a skilled technician to tune the systems with software and a laptop. This can require several trips as the environment of electronic noise often changes in a retail mall and the system will need adjustment to accommodate the xe2x80x9cnewxe2x80x9d environment.
What is needed is a system employing pseudorandom coding to prevent interferences from constant or periodic noise sources. A system that employs this vehicle and is constantly recalculating the environment will require less service visits and meet the needs of today""s retailers.
A method of reducing noise interference, in accordance with an inventive arrangement comprises the steps of: a) transmitting a string of non-periodic pulses; b) receiving a portion of the string of non-periodic pulses; and c) triggering an alarm if the portion of the string of non-periodic pulses is above a threshold value.
In accordance with the present invention, a transmitter sends out electromagnetic wave pulses in a non-periodic manner. The transmitter""s electromagnetic-wave pulses trigger a resonator within a marker (tag) that emits its own electromagnetic-wave signals similar to the signals coming in from the transmitter. A receiver processes the signals coming in from the tag and triggers an alarm if the received pulses are above a threshold value.
The string of non-periodic pulses can be a sequence of pseudorandom codes. The random transmitting sequence promotes a significant immunity to periodic interferences or constant noise operating in a surveillance area. The string of non-periodic pulses can also be mutually spaced and binary, in the form of 0 or 1, where 0 stands for null transmitting and 1 stands for valid transmitting. This string can also include several bits per cycle to measure the mean and standard deviation of the string of non-periodic pulses received.
The method can further include the step of recording the portion the portion of the string of non-periodic pulses. Alternatively, the method can further include the step of comparing the portion of the string of non-periodic pulses with the string of non-periodic pulses transmitted.
The method can further include the step of calculating a mean average and standard deviation of the string of non-periodic pulses received.
When the string of non-periodic pulses received is above a threshold value, which can be a predetermined number, the receiver will trigger an alarm. This predetermined number can be binary.
In an alternative embodiment of the present invention, a security system is provided that transmits a string of non-periodic pulses. A transmitter continuously transmits a string of non-periodic pulses, and a receiver receives at least a portion of the string of non-periodic pulses. The receiver triggers an alarm if the portion of the string of non-periodic pulses received is above a threshold.
As in the first inventive arrangement, the string of non-periodic pulses can be a sequence of random or pseudorandom codes; the string of non-periodic pulses can also be mutually spaced and binary, in the form of 0 or 1, where 0 stands for null transmitting and 1 stands for valid transmitting; and the string can also include several bits per cycle to measure the mean and standard deviation of the string of non-periodic pulses received.
The system can further include means for recording the portion of the string of non-periodic pulses. Alternatively, the system can further include means for comparing the portion of the string of non-periodic pulses with the string of non-periodic pulses transmitted.
The system can further include means for calculating a mean average and standard deviation of the string of non-periodic pulses received.
When the string of non-periodic pulses received is above a threshold value, which can be a predetermined number, the receiver will trigger an alarm. This predetermined number can be binary.
In a third aspect of the present invention, a security system is provided that transmits a string of non-periodic pulses. A transmitter continuously transmits a string of non-periodic pulses, and a receiver receives at least a portion of the string of non-periodic pulses. A circuit is coupled to the transmitter and receiver for comparing the portion of the string of non-periodic pulses with the string of non-periodic pulses transmitted; and whereby an alarm is triggered if the portion of the string of non-periodic pulses is above a threshold value.
In accordance with the preceding alterative, the string of non-periodic pulses can be a sequence of pseudorandom codes; the string of non-periodic pulses can also be mutually spaced and binary, in the form of 0 or 1, where 0 stands for null transmitting and 1 stands for valid transmitting; and the string can also include several bits per cycle to measure the mean and standard deviation of the string of non-periodic pulses received.